High-frequency wave attenuation spreads out seismic displacement and lowers surface acceleration.

Evidence

Imagine a section of rock cracking along a plane, displacing very suddenly under intense force. This sends a compression/rarefaction wave traveling through the rock at typically 7500 m/s. The shallow fault at Moodus makes it plausible that the easily attenuated high-frequency components of the wave survived to make it to the surface. The practical effect of the attenuation of the high frequencies is to lengthen the thickness of the disturbance traveling in the rock and spread the displacement over a longer time, lowering the acceleration when the disturbance reaches the surface. — Eric J. Heller, Why You Hear What You Hear- An…, 696